Rotational atherectomy device

Details Rotational atherectomy device Rotational atherectomy device

1999-01-04

2001-04-17

Buiz, Michael (Department: 3731)

Surgery

Instruments

Blood vessel, duct or teat cutter, scrapper or abrader

C242S430000

Reexamination Certificate

active

06217595

ABSTRACT:

FIELD OF THE INVENTION
The present invention provides an improved drive shaft for use with rotational atherectomy devices.
BACKGROUND OF THE INVENTION
A variety of techniques and instruments have been developed for use in the removal or repair of tissue in arteries and similar body passageways. A frequent objective of such techniques and instruments is the removal of atherosclerotic plaques in a patient's arteries. Atherosclerosis is characterized by a build-up of fatty deposits (atheromas) in the intimal layer (under the endothelium) of a patient's blood vessels. Very often over time, what Is initially deposited as relatively soft cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque. Such atheromas restrict the flow of blood, and therefore often are referred to as stenotic lesions or stenoses, the blocking material being referred to as stenotic material. If left untreated, such stenoses can cause angina, hypertension, myocardial infarction, strokes and the like.
Several kinds of atherectomy devices have been developed for attempting to remove some or all of such stenotic material. In one type of device, such as that shown in U.S. Pat. No. 4,990,134 (issued to Auth), a rotating burr covered with an abrasive cutting material such as diamond grit (diamond particles or dust) is carried at the distal end of a flexible drive shaft. One atherectomy device commercially available from Heart Technologies, Inc. of Bellevue, Washington, U.S.A. is sold under the trade name Rotablator. The design of the Rotablator device is, to a significant extent, based on the design described in the Auth patent and the Rotablator device is typically rotated at speeds in the range of about 150,000-190,000 rpm.
Auth's burr is made from a solid, inflexible metal which is physically attached to a flexible, trifilar, helically wound drive shaft. This solid burr must be kept relatively short in order to allow the burr to navigate the bends and curves in tortuous arteries. At the same time, it must be sufficiently long to ensure reliable fixation of the burr to the drive shaft.
Another type of atherectomy device is shown in U.S. Pat. No. 5,314,438 (issued to Shturman). This design provides a solution for the problems associated with fixation of a separate burr to a drive shaft by eliminating the burr altogether. The abrasive drive shaft atherectomy device disclosed in the above-mentioned Shturman patent typically is used over a guide wire and includes a flexible, elongated drive shaft made from one or more helically wound wires. Wire turns of the proximal segment of the drive shaft have a generally constant diameter, while wire turns of a segment of the drive shaft near its distal end have an enlarged diameter. At least part of the enlarged diameter segment includes an external coating of an abrasive material to define an abrasive segment of the drive shaft which, when rotated at high speeds, is usable to remove stenotic tissue from an artery.
Manufacturing some of the embodiments of the device shown in the above-mentioned Shturman patent can be relatively time-consuming. This is particularly true with respect to the embodiments of the device which use two helically wound layers, such as the one shown in
FIG. 8
of that reference. In that drawing and some of the other embodiments depicted in the Shturman patent, wire turns of the enlarged diameter segment of the drive shaft are supported by a bushing. Even though this bushing may be made of a flexible material, it does decrease somewhat the flexibility of the enlarged diameter abrasive segment of the drive shaft. Unless a bushing within the enlarged diameter segment is used, though, adjacent wire turns of this segment can fall out of alignment with one another when the enlarged diameter segment of the drive shaft is bent around a curve.
SUMMARY OF THE INVENTION
The present invention provides a novel rotational atherectomy device which includes an improved drive shaft and a method of making the same. Certain embodiments of the invention provide improvements over the atherectomy device taught in the Shturman patent mentioned above.
In accordance with a first embodiment, a rotational atherectomy device of the invention includes a flexible, elongated drive shaft having a central lumen for receipt of a guide wire therein around which the drive shaft may be rotated. The drive shaft has inner and outer co-axial wire layers helically wound in opposite directions so that the outer layer tends to radially contract and the inner layer tends to radially expand when the drive shaft is rotated in a predetermined direction. The outer layer of this embodiment comprises a mono-filar helically wound coil and the inner layer comprises a multi-filar helically wound coil received in the lumen of the outer layer. As explained below, this construction makes it easier to cost-effectively manufacture an appropriately shaped device with suitable mechanical properties. This drive shaft has proximal, intermediate and distal segments, with the outer layer of the intermediate segment of the drive shaft having a diameter which gradually increases distally through its proximal portion and gradually decreases distally through its distal portion, thereby defining an enlarged diameter segment of the drive shaft. At least part of this enlarged diameter segment desirably includes an external coating of an abrasive material to define an abrasive segment of the drive shaft which functions as an enlarged diameter tissue removal segment of the device. If wire turns along the distal portion of the intermediate segment are spaced from one another, then the abrasive material is optimally bonded to individual wire turns along at least part of the distal portion of the intermediate segment. If the wire turns of the outer layer along the abrasive segment are not spaced from one another, one can apply abrasive material using a binder which not only bonds abrasive material to the wire turns, but also bonds at least some of the wire turns to one another along at least part of the abrasive segment.
In keeping with a further embodiment of the invention, a rotational atherectomy device includes at least two helically wound wires forming inner and outer co-axial wire layers which preferably are helically wound in opposite directions, as mentioned above. The outer layer has an increased diameter along at least part of its length to define an enlarged diameter segment of the drive shaft. The precise shape of this enlarged diameter segment of the drive shaft can be varied. In accordance with this embodiment, wire turns of the inner layer of the drive shaft are spaced from one another along the enlarged diameter segment of the drive shaft. This has been found to further improve flexibility of the device while maintaining an appropriate shape in the enlarged diameter segment when the drive shaft is bent in operation, e.g. to keep wire turns of the enlarged diameter segment from falling out of alignment with one another when the drive shaft is bent or flexed to track curvatures of an artery or other vascular structure.
One preferred rotational atherectomy device of the invention includes a flexible, elongated drive shaft having at least two helically wound wires forming inner and outer co-axial wire layers helically wound in opposite directions so that the outer layer tends to radially contract and the inner layer tends to radially expand when the drive shaft is rotated in a predetermined direction. The drive shaft has proximal, intermediate and distal segments, with wire turns of the outer layer of the intermediate segment of the drive shaft having diameters that increase distally at a generally constant rate through a proximal portion of such intermediate segment thereby forming generally the shape of a cone. At least some adjacent wire turns of the inner layer of the intermediate segment of the drive shaft are spaced from one another, improving flexibility of the intermediate segment of the drive shaft. At least part of a distal portion of the intermediate segment o

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